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soybean cultivation (no-till or conventional) causes only small losses and may even
increase SOC and total N concentrations (Frazão et al. 2010).
Some Ustoxes with low clay contents (15%-20%) and a weak granular or blocky
structure occur in association with Quartzipsamments and have similar properties
and land use restrictions. In the Cerrado, these Ustoxes are called Latossolo textura
média and probably comprise a significant area whose extent is not exactly known
and are especially common in the São Francisco river basin.
3.1.4 u ltiSolS
Ultisols comprise ~15% of the Cerrado land area (Adámoli et al. 1986), and, as
Oxisols, are developed mostly under ustic soil moisture regimes. However, research
information on Cerrado Ultisols is rather scanty compared with those in the coastal
region of Brazil, where these soils are more common. In the Brazilian System, these
soils are classified as Argissolos and Nitossolos (formerly Podzólicos ; Embrapa
2006), for their argillic or kandic horizon with low-activity clays. Most of these
soils can be classified as Kandiustults, Kanhaplustults, Rodhustults, and Haplustults
in Soil Taxonomy (Soil Survey Staff 2010). Although Ustults can develop from
the same rocks as Ustoxes, they are more frequently associated with granites and
gneisses and rarely with sandstones. Thus, sand contents of these soils are neither
too low nor too high. Ustults can occur in association with Ustoxes, but they typi-
cally form on midslopes and small summits of hilly terrains. The predominant clay
minerals are similar to those in Ustoxes, but in contrast, Fe/Al oxide contents are
relatively low and kaolinite almost always predominates in Ustults. Therefore, the
granular structure in Ustults is exceedingly rare and restricted to the surface layer,
and subangular or angular blocky structure predominates in most horizons. A practi-
cal consequence of the blocky structure is that soil bulk density is ~20% higher in
uncultivated Ustults than Ustoxes, to 1-m depth (Araujo, M.A. et al. 2011), and root
penetration is severely impeded in the subsoil horizons. In general, most Cerrado
Ustults do not have a strong textural gradient and are thus distinguished by high
bulk density and/or abundance of clay films on ped surfaces. Mechanical strength
is also high, often necessitating subsoiling, and land use-induced compaction can
severely inhibit root growth. Soil depth and internal drainage are also much less
than in Ustoxes, which aside from the hilly terrain is highly conducive to sheet or
interrill erosion (Carvalho et al. 2008). On the other hand, leaching of bases can be
lower (Curi, N., personal communication) and natural nutrient levels higher than
those in Ustoxes. It is because of these factors that these soils are more commonly
used for pastures, forest plantations, and perennial crops such as coffee, especially
in southwestern Minas Gerais.
3.1.5 o ther r elevant S oil t ypeS
Soils with ironstone and/or plinthic features, as defined in Soil Taxonomy (Soil
Survey Staff 2010), can be classified as Ustoxes, Ustults, Plinthic Quartzipsamments,
and Petraquepts. Soils with these features cover ~9% of the Cerrado area, and 6%
may have aquic soil moisture regimes (Adámoli et al. 1986). The Brazilian System
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